1. Field of the Invention
The present invention relates to a hot-water supply apparatus, which stores hot water in a hot-water tank by circulating water of a hot-water tank through a water-heat exchanger of a heat pump refrigeration cycle.
2. Description of the Related Art
There is a hot-water supply apparatus, which has a heat pump refrigeration cycle having a compressor, a water-heat exchanger and an outdoor heat exchanger, and stores hot water in a hot-water tank by circulating water of a hot-water tank through a water-heat exchanger by operating a pump.
In this hot-water supply apparatus, frost gradually forms on the surface of an outdoor heat exchanger functioning as an evaporator, and it is necessary to eliminate the frost from the outdoor heat exchanger periodically or as needed.
As a method of eliminating frost, there is a known method called reverse cycle defrosting, which reverses the flow of refrigerant in a heat pump refrigeration cycle, and supplies a high-temperature refrigerant ejected from a compressor directly to an outdoor heat exchanger.
There is another method (Jpn. Pat. Appln. KOKAI Publication No. 2004-183908), which causes hot water of a hot-water tank to flow to a water-heat exchanger, and transfers the heat of the hot water to the refrigerant, while performing a reverse cycle defrosting. This method can reduce the time required to defrost, compared with the method of executing only a reverse cycle defrosting.